Ocular myasthenia gravis induced by human acetylcholine receptor epsilon subunit immunization in HLA DR3 transgenic mice

Abstract

Extraocular muscles (EOM) are preferentially involved in myasthenia gravis (MG) and acetylcholine receptor (AChR) antibody positive MG patients may occasionally present with isolated ocular symptoms. Although experimental autoimmune myasthenia gravis (EAMG) induced by whole AChR immunization closely mimics clinical and immunopathological aspects of MG, EOM are usually not affected. We have previously developed an EAMG model, which imitates EOM symptoms of MG by immunization of human leukocyte antigen (HLA) transgenic mice with alpha or gamma-subunits of human AChR (H-AChR). To investigate the significance of the epsilon-subunit in ocular MG, we immunized HLA-DR3 and HLA-DQ8 transgenic mice with recombinant H-AChR epsilon-subunit expressed in Escherichia coli. HLA-DR3 transgenic mice showed significantly higher clinical ocular and generalized MG severity scores and lower grip strength values than HLA-DQ8 mice. H-AChR epsilon-subunit-immunized HLA-DR3 transgenic mice had higher serum anti-AChR antibody (IgG, IgG1, IgG2b, IgG2c and IgM) levels, neuromuscular junction IgG and complement deposit percentages than epsilon-subunit-immunized HLA-DQ8 transgenic mice. Control mice immunized with E. coli extract or complete Freund adjuvant (CFA) did not show clinical and immunopathological features of ocular and generalized EAMG. Lymph node cells of epsilon-subunit-immunized HLA-DR3 mice showed significantly higher proliferative responses than those of epsilon-subunit-immunized HLA-DQ8 mice, crude E. coli extract-immunized and CFA-immunized transgenic mice. Our results indicate that the human AChR epsilon-subunit is capable of inducing myasthenic muscle weakness. Diversity of the autoimmune responses displayed by mice expressing different HLA class II molecules suggests that the interplay between HLA class II alleles and AChR subunits might have a profound impact on the clinical course of MG. (C) 2015 European Federation of Immunological Societies. Published by Elsevier B.V. All rights reserved.